1. Field of the Invention
The subject matter disclosed herein relates generally to the field of fluorescent materials and more specifically to an LED module comprising quantum dot composite fluorescent particles.
2. Description of the Related Art
A quantum dot refers to a semiconductor nano-structure that bonds excitons in three spatial directions. Quantum dots can be divided into three categories: a colloidal quantum dot, a self-assembled quantum dot, and an electric field confinement quantum dot. Quantum dots produce multiple unique electrical and optical properties due to the quantum restriction effect of an electron wave function caused by the size of the quantum dot being less than or close to the Bohr radius of the exciton. Therefore, quantum dot technology shows huge potential in disciplines such as biochemistry, cell biology, immunochemistry and the like. It has been applied in lasers, single electron transistors, detectors, biological stains, medical diagnoses, DNA sequence determination and immunoassays, etc.
The quantum dot cannot normally be used directly because it has relatively weak stability in ambient circumstances. The quantum dots may cluster causing fluorescence quenching and energy transfer since the nano-size surface energy is large. Meanwhile, the colloidal layer and surface element, such as S, of the colloidal quantum dot is easily corroded to retain a defect level, form a non-radiative transition channel, and cause fluorescence fading. Most physicochemical environments will cause fluorescence quenching to the quantum dot. Therefore, how to use the quantum dot is presently a hot and critical issue.
During the application process, general practice is to directly disperse the quantum dots into a polymer matrix to obtain a fluorescence composite material and form a simple “quantum dots-matrix materials” structure. The composite material substantially maintains the fluorescence characteristic of the colloidal quantum dot. The composite material can then be directly integrated with a blue LED to obtain white lights, or to obtain a multicolor spectrum converted by the quantum dot, which can be directly applied to displays and lightings, respectively.
Quantum dots are presently used by first dispersing the colloidal quantum dots in silica gel directly through a manner of stirring, then attaching the silica gel on the LED through a manner of dispensing. In the method, red-green quantum dots can be used to obtain blue/green/red white LEDs. Similarly, yellow quantum dots such as CuInS2 series quantum dots can also be used to obtain white LEDs. Additionally, white LEDs can also be obtained by using the quantum dots coated with phosphor powder. However, this method has a compatibility problem between the colloidal quantum dot and the silica gel. Because the surface ligands of the quantum dots are not compatible with the silica gel matrix materials, fluorescence quenching caused by the aggregation of the quantum dots and the peeling off of the surface ligands will usually appear. Meanwhile, the silica gel has poor blocking properties against water and oxygen; therefore, during operation of a quantum dots-related LED device, erosion caused by water and oxygen, particularly under light exposure, causes fluorescence fading of the quantum dot so that the service life of the device is short. Further, the surface of the quantum dot (inorganic layer and organic ligand) contains sulfur which will react with the commercial silica-gel-curing platinum catalyst at present, so that the silica gel cannot be cured.
Another method is to disperse the quantum dots in a polymer material in order to obtain a quantum dot light conversion film, and then seal the film on a blue light chip using remote packaging. Although this method improves the compatibility problem between the quantum dot and the matrix materials, the polymer's ability to block the water and oxygen is still limited. Therefore, during the long term operating period, the quantum dot will still face the erosion problem caused by photooxygenation. In order to solve the problems caused by water and oxygen, a silicon dioxide/polyethylene pyrrolidone material is employed as a remote packaged blocking layer. The invasion of water and oxygen is blocked by providing surface protection on the composite film, and adding a film with better water-blocking and oxygen-blocking capacity in the upper and lower layers, so that the damage on the surface of the quantum dot is reduced. Although this method can block water and oxygen to a certain extent, the ligand wearing and conglobation effects caused by the incompatibility problem between the outer surface of the quantum dot and the matrix cannot be prevented, thus affecting the stability and reliability of a light emitting device. It is worth pointing out that the luminous efficacy of the remote-packed LED is poorer than that of on-chip packing.
Therefore, for the use of quantum dots with high luminous efficiency and high stability in LED devices, the following problems must be resolved. First, the quantum dot must not destroy the quantum efficiency during self-surface treatment or when composited with other materials. Second, the ambient environment of the quantum dot must be compatible with the surface of the quantum dot, thereby preventing the aggregation of the quantum dot and the peeling off of the ligand. Third, a blocking layer must be configured to prevent erosion from molecules like water vapor and oxygen on the surface of the quantum dot.
Chinese patent application number 201510576368 discloses a fluorescent quantum dot micro-nano packaged composite material structure, wherein the composite material structure includes a fluorescent quantum dot, a mesoporous material having a nanometer lattice structure, and a blocking layer. The fluorescent quantum dot is distributed in the mesoporous material, and the blocking layer is coated on the outer surface of the mesoporous material. Although the blocking layer can better block water and oxygen, water and oxygen will still remain in the mesoporous material. Moreover, the coating effect of the blocking layer is far lower than the theoretically expected effect and thus, the blocking effect on the water and oxygen is not ideal. Therefore, it is desirable to improve the prior art to obtain a quantum dot composite material having better water-blocking and oxygen-blocking effects and higher efficiency.
3. Objects and Advantages
It is a principal object and advantage of the present invention to provide a quantum dot composite fluorescent particle having excellent water-blocking and oxygen-blocking effects.
It is a further object and advantage of the present invention to provide an LED device using the quantum dot composite fluorescent particle as a light conversion material.
It is another object and advantage of the present invention to provide water-blocking and oxygen-blocking material that fills the gaps between quantum dots and mesoporous material, so that the matrix materials of the quantum dots are more compact, and the water-blocking and oxygen-blocking characteristics of the quantum dot composite fluorescent particle are greatly improved; therefore, the stability of the quantum dot composite fluorescent particle is improved.
Yet another object and advantage of the present invention is to provide metal nanoparticles that can help the quantum dots capture more blue lights and improve the utilization ratio of the blue lights. During actual production, the use of the quantum dots for obtaining the same light conversion effect can be reduced, thus reducing the use of heavy metal in the quantum dots in order to be more environmentally friendly.
A further object and advantage of the present invention is to provide metal nanoparticles that improve the fluorescence intensity of the quantum dot due to surface plasmas produced by the regular motion of the free electrons of the metal nanoparticles under the action of an external electromagnetic field that can greatly enhance the electromagnetic field surrounding the particles. When the frequency of incident lights is consistent with the natural frequency of the free electrons of the metal nanoparticles, surface plasma resonance is produced, which enhances a local field to maximum while this enhanced local field enhances the excitation rate and the luminous intensity of the quantum dots near the surface of the metal nanoparticles.
It is another object and advantage of the present invention to provide metal nanoparticles that improve the fluorescence intensity of the quantum dot with non-radiative energy transfer that occurs between the quantum dots and the metal nanoparticles during the coupling radiation process of the metal nanoparticles and the quantum dots, and is coupled into LSPR energy by excited quantum dots while the LSPR is radiated to a far field in turn.
Yet another object and advantage of the present invention is to provide a preparation process that employs no chemical machining or chemical treatment, and retains the fluorescence characteristic of the quantum dots, including emission wavelength and fluorescence efficiency, so that the quantum dot composite fluorescent particle has a very high quantum efficiency.
A further object and advantage of the present invention is to provide a quantum dot composite fluorescent particle that has a mesoporous structure, thus greatly reducing the efficiency fading or quenching caused by the aggregation of the quantum dots in fluorescence particles.
It is another object and advantage of the present invention to provide a quantum dot composite fluorescent particle that has a blocking layer structure, which reduces and even completely blocks the quantum dots from being contacted with water and oxygen, thereby improving the service efficiency, enabling the quantum dot composite fluorescent particle and the LED module thereof to have excellent service lives, and allowing the quantum dot composite fluorescent particle to be directly used for commercializing.
An additional object and advantage of the present invention is to provide a quantum dot composite fluorescent particle and LED chip that can be directly packaged in a chip contact manner, which greatly improves the luminous efficacy of the LED.
Yet another object and advantage of the present invention is to provide a quantum dot composite fluorescent particle that is directly prepared to obtain a blue/green/red white LED for displaying and may also be matched with phosphor powder to obtain a white LED for lighting.
Other objects and advantages of the present invention will in part be obvious and in part appear hereinafter.